全文获取类型
收费全文 | 11464篇 |
免费 | 1835篇 |
国内免费 | 1647篇 |
专业分类
化学 | 8691篇 |
晶体学 | 161篇 |
力学 | 627篇 |
综合类 | 99篇 |
数学 | 1170篇 |
物理学 | 4198篇 |
出版年
2024年 | 59篇 |
2023年 | 252篇 |
2022年 | 475篇 |
2021年 | 454篇 |
2020年 | 559篇 |
2019年 | 562篇 |
2018年 | 441篇 |
2017年 | 462篇 |
2016年 | 566篇 |
2015年 | 588篇 |
2014年 | 689篇 |
2013年 | 881篇 |
2012年 | 959篇 |
2011年 | 1033篇 |
2010年 | 740篇 |
2009年 | 660篇 |
2008年 | 787篇 |
2007年 | 606篇 |
2006年 | 572篇 |
2005年 | 507篇 |
2004年 | 375篇 |
2003年 | 333篇 |
2002年 | 379篇 |
2001年 | 264篇 |
2000年 | 227篇 |
1999年 | 197篇 |
1998年 | 152篇 |
1997年 | 131篇 |
1996年 | 138篇 |
1995年 | 143篇 |
1994年 | 135篇 |
1993年 | 116篇 |
1992年 | 81篇 |
1991年 | 68篇 |
1990年 | 61篇 |
1989年 | 63篇 |
1988年 | 37篇 |
1987年 | 34篇 |
1986年 | 37篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1959年 | 2篇 |
1957年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
烷基季铵盐插层剂的合成及应用 总被引:1,自引:0,他引:1
Three novel intercalation agents were synthesized for the first time, which arose from oleic acid diethylenetriamine or triethylenetetramine 3 - chloro - 2 - hydroxypropy trimethylammonium choride (CHPTA) and chloroethanol. Organophilic vermicullites were synthesized from sodium type vermiculite by cation exchange with new intercalation agents. The results of X - ray diffraction study showed that the gallery distance of the organophilic vermiculite was enlarged from 1 nm to 5 nm or more. A new idea of making design for intercalation agent was provided. 相似文献
44.
45.
46.
Reaction solutions of selectfluor (1) with triphenylethylene (4a) and tetraphenylethylene (4b) were monitored by ESI-MS and ESI-MS/MS. Detection and characterization of the key radical cationic intermediates 5a.+ and 5b.+) fully supports the SET mechanism in electrophilic fluorination as depicted above. [reaction: see text] 相似文献
47.
48.
In the degassing process of transformer oil with ultrasonic waves ,decompostition of the oil was observed.Light hydrocarbons,including methane,ethane,ethylene ,aceylene,propane etc,were found to be released continuously from the oil into headspace within a closed vial placed in an ultrasonic field ,The gases came from decomposition of hydrocarbon molecules under cavitation effect. 相似文献
49.
(1)测定了醋酸十二烷基铵(DAA)在CAB-O-SIL上的吸附,其等温线属双平台或LS型[1-3,5];(2)NaCl的存在使DAA的吸附增加.但不影响其低浓度下第一平台的吸附量;HCl的存在则在全浓度范围内抑制了DAA的吸附,(3)测定了CAB-O-SIL颗粒在上述各溶液中的悬浮液的稳定性;(4)根据表面形成小胶团的吸附理论(即二步模型产)[2,3,5,],并借助电导跟踪溶液中发生的变化,满意地解释了吸附和聚沉的实验结果. 相似文献
50.
We derive exact properties of the inhomogeneous electron gas in the asymptotic classically forbidden region at a metal–vacuum interface within the framework of local effective potential energy theory. We derive a new expression for the asymptotic structure of the Kohn–Sham density functional theory (KS‐DFT) exchange‐correlation potential energy vxc(r) in terms of the irreducible electron self‐energy. We also derive the exact asymptotic structure of the orbitals, density, the Dirac density matrix, the kinetic energy density, and KS exchange energy density. We further obtain the exact expression for the Fermi hole and demonstrate its structure in this asymptotic limit. The exchange‐correlation potential energy is derived to be vxc(z → ∞) = ?αKS,xc/z, and its exchange and correlation components to be vx(z → ∞) = ?αKS,x/z and vc(z → ∞) = ?αKS,c/z, respectively. The analytical expressions for the coefficients αKS,xc and αKS,x show them to be dependent on the bulk‐metal Wigner–Seitz radius and the barrier height at the surface. The coefficient αKS,c = 1/4 is determined in the plasmon‐pole approximation and is independent of these metal parameters. Thus, the asymptotic structure of vxc(z) in the vacuum region is image‐potential‐like but not the commonly accepted one of ?1/4z. Furthermore, this structure depends on the properties of the metal. Additionally, an analysis of these results via quantal density functional theory (Q‐DFT) shows that both the Pauli Wx(z → ∞) and lowest‐order correlation‐kinetic W(z → ∞) components of the exchange potential energy vx(z → ∞), and the Coulomb Wc(z → ∞) and higher‐order correlation‐kinetic components of the correlation potential energy vc(z → ∞), all contribute terms of O(1/z) to the structure. Hence correlations attributable to the Pauli exclusion principle, Coulomb repulsion, and correlation‐kinetic effects all contribute to the asymptotic structure of the effective potential energy at a metal surface. The relevance of the results derived to the theory of image states and to KS‐DFT is also discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献